In the technique of laser enrichment as shown, for example, in U.S. Pat. No. 3,772,519, or patent applications, Ser. No. 328,954, filed Feb. 2, 1973 and Ser. No. 469,407, filed May 13, 1974, all assigned to the same assignee as the present application and all incorporated herein by reference, pulsed laser radiation is employed for isotopically selective excitation of a uranium vapor flow. In order to provide an increased pulse rate in the applied laser radiation for greater system efficiency, it has been suggested, as for example shown in copending U.S. Pat. application Ser. No. 438,029, filed Jan. 30, 1974, assigned to the same assignee as the present application and incorporated herein by reference, to employ a system of rotating optics to combine a time sequence of radiation pulses from a plurality of radiation paths onto a single combined path of radiation of increased pulse repetition rate. For use in this system, apparatus is desired for generating plural channels of pulsed laser radiation with the pulses for each channel related in a predetermined time pattern, and with well maintained stability and spectral consistency in the laser radiation of each channel so that the combined beam is suitable for efficient, isotopically selective photoexcitation.